Laser annealing apparatus

ABSTRACT

A laser annealing apparatus for sequential lateral solidification (SLS) to uniformly crystallize silicon on an entire silicon substrate by minimizing the dislocation of the silicon substrate during laser beam irradiation is disclosed. During the laser annealing, a vacuum chuck holds the silicon substrate on a movable stage. The device includes a laser source, an optical system patterning the shape and energy of a laser beam irradiated from the laser source, a vacuum chuck supporting a silicon substrate, and a movable stage supporting the vacuum chuck as well as transferring the vacuum chuck in a predetermined direction. Accordingly, the apparatus improves the degree of crystallization because it is able to uniformly carry out SLS on an entire surface of the silicon substrate.

This is a divisional of application Ser. No. 09/697,510, filed Oct. 27,2000, now U.S. Pat. No. 6,514,339.

BACKGROUND OF THE INVENTION

1. Field of Invention

A laser annealing apparatus is used for sequential lateralsolidification (SLS) to crystallize silicon.

2. Discussion of Related Art

Sequential laser solidification (SLS) is used for crystallizing asilicon film by using the fact that silicon grains grow perpendicularlyto an interface between a liquid silicon region and a solid siliconregion, i.e., into the molten silicon or melt zone. SLS differs from aconventional laser crystallization by patterning a laser beam to have apredetermined width and a predetermined shape. The SLS uses a mask forpatterning a laser beam.

The process of crystallizing a silicon film by SLS is briefly explainedbelow.

First, a silicon film is irradiated with a laser beam having apredetermined shape with sufficient energy to entirely melt a portion ofthe silicon. The silicon portion exposed to the laser beam resolidifiesshortly after melting. During this process, silicon grains grow at aninterface between a solid silicon region not exposed to the laser beamand a liquid silicon region exposed to the laser beam, and in adirection toward the liquid silicon region.

Second, the silicon film is irradiated with a laser beam having the sameenergy as previously used. The second irradiation occurs after theamorphous silicon film has been displaced to a distance shorter than thegrowing length of a silicon grain formed by the first laser beamirradiation. As a result, the silicon portion exposed to the laser beammelts, and then the silicon grain grows similarly as it did in the firstlaser beam irradiation. In this case, the silicon grain formed by thefirst laser beam irradiation works as a crystallization seed at theinterface and continues to grow in the same direction as the advancingmelt zone. Thus, the silicon grain grows toward the displacing directionof the laser beam.

The silicon grain is grown to the desired length by repeating n timesthe silicon crystallizing steps of displacing an amorphous silicon film,melting the silicon film by laser beam irradiation and solidifying themelted silicon. The silicon grain grows in the direction of laserscanning from the place of initial formation.

Accordingly, laser crystallization using SLS results in greatlyextending the silicon grain size.

A typical process chamber used in a laser annealing system according tothe related art is shown in FIG. 2. The process chamber is constructedwith a chamber window 20-2 and a chamber wall 20-1. A support 22supports a silicon substrate which will be irradiated with a laser beamfor laser crystallization. A movable stage 21 moves the siliconsubstrate 23 in a predetermined direction.

In FIG. 2, the interior process chamber is sealed and evacuated to forma vacuum for laser crystallization. The chamber window 20-2 becomes anentrance through which a laser beam patterned by a laser optical systempasses to the inner space of the process chamber.

In laser crystallization using SLS, the silicon substrate 23 isirradiated with a laser beam with a predetermined repetition rate, andthe movable stage 21 moves in a predetermined direction. As a result,the silicon substrate 23 is scanned entirely by the laser beam.

SLS requires precise control of system variables such as transfer,uniform evenness and the like for allowing continuous growth of silicongrains without stopping. However, the conventional technology supportsthe silicon substrate 23 using only the support 22. The utilization ofthe support 22 causes the silicon substrate 23 to be unstable. A furthercomplicating factor is the unevenness of the surface of the siliconsubstrate. The focal point of the laser is fixed, but the surface of thesilicon substrate is uneven. As a result, the laser beam cannotuniformly irradiate the silicon substrate 23 so as to permit thecontinuous growth of silicon grains. The variation of the distancebetween the silicon substrate and the focus of the laser beam results inunevenness of laser energy with which the silicon substrate is supplied.The resulting laser crystallization, which should be carried out withcontinuous and uniform conditions, produces a poor result.

Further, the width of a laser beam with which the silicon substrate isirradiated varies in accordance with the distance between the siliconsubstrate and a focus of the laser beam. The narrower the width of thelaser beam becomes, the greater the influence of the distance becomes.

Moreover, when the silicon substrate is transferred by the movablestage, minute changes of the location of silicon substrate occur.Considering that SLS is carried out under the condition that the widthof the patterned laser beam and the transferring interval are withinseveral μm, the minute dislocations of the silicon substrate fail tocontinuously grow the silicon grain without stopping. Thus,discontinuation of crystallization may result instead of continuousgrowth of the silicon grain.

As has been shown, the conventional SLS technology is hampered bydiscontinuities which inhibit the continuous growth of silicon grains.As a result, a technology is needed which provides smooth and even laserprocessing of the silicon substrate to yield continuous growth of largesilicon grains using SLS.

SUMMARY OF THE INVENTION

The invention is directed to a laser annealing apparatus thatsubstantially eliminates many of the problems due to the limitations anddisadvantages of the prior art.

The invention, in part, provides a laser annealing apparatus capable ofperforming uniform laser crystallization on an entire silicon substrateby minimizing the dislocation of the silicon substrate during laser beamirradiation. The minimized dislocation can be achieved by installing avacuum chuck holding the silicon substrate in a movable stage.

The invention, in part, provides a laser annealing apparatus which cancarry out uniform laser crystallization on an entire silicon substrateby minimizing the unevenness of the silicon substrate. The minimizedunevenness can be achieved by using a vacuum chuck that holds thesilicon substrate using a vacuum attachment.

To achieve these and other advantages and in accordance with the purposeof the invention, as embodied and broadly described, the inventionincludes a laser source, an optical system patterning a shape and anenergy of a laser beam irradiated from the laser source, and a vacuumchuck supporting a silicon substrate on which laser crystallization isperformed by the patterned laser beam. The vacuum chuck holds thesilicon using a vacuum. A movable stage supports the vacuum chuck andfunctions to move the vacuum chuck in a predetermined direction.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiments of the invention, andtogether with the description serve to explain the principle of theinvention.

FIG. 1 shows a schematic of a laser annealing apparatus using SLS;

FIG. 2 shows a schematic of a process chamber in a laser annealingsystem according to the conventional art;

FIG. 3 shows a schematic of a process chamber in a laser annealingsystem according to the invention; and

FIG. 4 shows the up and down movement of a silicon substrate in theprocess chamber shown in FIG. 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Advantages of the present invention will become more apparent from thedetailed description given herein after. However, it should beunderstood that the detailed description and specific examples, whileindicating preferred embodiments of the invention, are given by way ofillustration only, since various changes and modifications within thespirit and scope of the invention will become apparent to those skilledin the art from this detailed description.

FIG. 1 shows a laser annealing apparatus for use in sequential lateralsolidification (SLS).

When crystallizing a silicon film by SLS, a laser beam is patterned to apredetermined shape, and the silicon film is continuously irradiatedwith the patterned laser beam.

For crystallizing the silicon film, an unpatterned initial laser beamirradiates from a laser source 10 and passes through an attenuator 11, ahomogenizer 12, and a field lens 13, thereby both controlling the energyof and condensing the laser beam.

The laser beam is subsequently patterned to a predetermined shape bypassing the beam through a mask 14. After the patterned laser beam haspassed through an object lens 15, the laser beam irradiates a siliconfilm 17 placed on a translation stage 16 inside a process chamber 20.Although it is formed over a substrate in a liquid crystal display, thesilicon film 17 will be referred to as a silicon substrate in thefollowing description. Mirrors 19-1, 19-2, and 19-3 are also present tocontrol the path of the laser beam in the laser optical system.

FIG. 3 schematically shows a process chamber of a laser annealingapparatus according to an embodiment of the present invention.

FIG. 3 shows elements of a conventional structure of a process chamberwhere a chamber window 30-2 and a chamber wall 30-1 provide an innerspace of the process chamber. The chamber window 30-2 becomes anentrance through which a laser beam patterned by a laser optical systempasses to the inner space of the process chamber.

In the process chamber, a silicon substrate 37 is installed on a movablestage 31 in the process chamber. A vacuum chuck 33 supports the siliconsubstrate 37 by utilizing vacuum attachment of the silicon substrate 37to the movable stage 31. A member, e.g., a moving cylinder, 35 isinstalled in the vacuum chuck 33. The member 35 is used for separatingand coupling the silicon substrate 37 from and with the vacuum chuck 33by moving up and down, and the member 35 is installed in the vacuumchuck 33. The movable stage 31 fixes the vacuum chuck 33 as well astransfers the silicon substrate 37 to the left direction, to the rightdirection or horizontally.

The silicon substrate 37 is irradiated with a laser beam using apredetermined repetition rate, while the movable stage 31 continuouslymoves in a predetermined direction. As a result, the silicon substrate37 is scanned entirely by the laser beam.

The vacuum chuck 33 in the structure of the present invention causes thesilicon substrate 37 to adhere strongly. As a result, the siliconsubstrate is in a very stable state. Thus, any dislocation of thesilicon substrate 37 is substantially prevented regardless of thetransferring movement of the movable stage.

Moreover, the entire bottom face of the silicon substrate 37 is held bythe vacuum chuck 33, and this strong attachment allows the siliconsubstrate to maintain its evenness to a certain degree despite theunevenness of the surface of the silicon substrate.

FIG. 4 explains the up and down movement of a silicon substrate in theprocess chamber shown in FIG. 3.

FIG. 4 shows the loading of the silicon substrate 37 when the member,e.g., moving cylinder, 35 protrudes over the vacuum chuck 33. In thismode, the silicon substrate 37 is put on the member 35 by using a robotarm 39. Then, the member 35 retracts to place the silicon substrate 37on the vacuum chuck 33. As shown in FIG. 3, the silicon substrate 37 isheld or coupled by activating the vacuum chuck 33.

By the above-explained procedure, silicon crystallization by SLS iscarried out while the silicon substrate is held by a vacuum on thevacuum chuck.

When unloading the silicon substrate, the silicon substrate 37 isreleased by breaking the vacuum of the vacuum chuck 33. The member 35then rises to decouple or separate the silicon substrate 37 from thevacuum chuck 33 so as to leave an interval between the vacuum chuck 33and the silicon substrate 37. The silicon substrate 37 is then separatedfrom the member 35 by the robot arm 39.

As described above, the laser annealing apparatus, according to thepresent invention, allows an optimal SLS process by providing a uniformand stable silicon substrate by holding the silicon substrate onto achuck by using a vacuum.

The advantages achieved by the invention include maintaining evenness ofthe silicon substrate surface and supporting the silicon substratestrongly by holding or coupling an entire face of the silicon substratein a vacuum state by using a vacuum chuck. Thus, the entire surface ofthe silicon substrate undergoes uniform exposure to a laser by leaving ahighly controlled predetermined distance between the silicon substrateand the focus of a laser beam.

Accordingly, the invention markedly improves the degree ofcrystallization because it is able to carry out SLS on an entire surfaceof a silicon substrate uniformly.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in a laser annealing apparatusof the present invention without departing from the spirit or scope ofthe invention. Thus, it is intended that the foregoing descriptions andspecific embodiments shown herein are merely illustrative of the bestmode of the invention and the principles thereof, and that modificationsand additions may be easily made by those skilled in the art withoutdeparting from the spirit and scope of the invention, which is thereforeunderstood to be limited only by the scope of the appended claims.

1. A laser annealing apparatus comprising: a laser source, a vacuumchuck supporting a substrate, and a movable stage supporting the vacuumchuck.
 2. A laser annealing apparatus comprising: a laser source, avacuum chuck supporting a substrate, a movable stage supporting thevacuum chuck, and at least one movable member installed in the vacuumchuck, the movable member being operable to move up and down in thevacuum chuck to couple and decouple the substrate with the vacuum chuck.3. The apparatus according to claim 2, wherein the member is a cylinder.4. The apparatus according to claim 1, which further comprises, betweenthe laser source and the substrate: an attenuator, a homogenizer and afield lens.
 5. The apparatus according to claim 1, which furthercomprises, between the field lens and the substrate: a mask and anobject lens.
 6. A laser annealing apparatus comprising: a laser source,a vacuum chuck supporting a substrate, a movable stage supporting thevacuum chuck, and a process chamber containing the vacuum chuck, themovable stage and the substrate.
 7. The apparatus according to claim 6,wherein the process chamber comprises a chamber window and a chamberwall providing an inner space.
 8. A laser annealing apparatuscomprising: a laser source, a vacuum chuck supporting a substrate, amovable stage supporting the vacuum chuck, and a robot arm to place andseparate the substrate on the vacuum chuck.
 9. The apparatus accordingto claim 8, wherein the substrate is silicon.
 10. A laser annealingapparatus comprising: a laser source, a vacuum chuck supporting asubstrate, and a movable stage supporting the vacuum chuck, wherein thesubstrate is silicon.
 11. An apparatus for crystallizing anon-crystalline material, comprising: a laser source for irradiatinglaser beam to a portion of the non-crystalline material; a movable stagefor moving the non-crystalline material to irradiate the laser beam tothe next portion of the non-crystalline material, thereby the irradiatedportion of the non-crystalline material is sequentially crystallizedfrom the crystalline portion of the non-crystalline material; a vacuumchuck formed in the movable stage to adhere the substrate; and loadingmember for loading the substrate to the movable stage.
 12. The apparatusaccording to claim 11, further comprising: laser patterning means forpatterning the laser beam emitted from the laser to crystallize aportion of the non-crystalline material corresponding to the patternedlaser beam.
 13. The apparatus according to claim 12, wherein the laserpatterning means includes a patterned mask.
 14. The apparatus accordingto claim 11, wherein the non-crystalline material includes an amorphoussilicon.
 15. The apparatus according to claim 14, wherein the amorphoussilicon includes a substrate.
 16. A laser annealing apparatuscomprising: a laser source; a movable stage supporting a substrate; avacuum chuck for adhering the substrate to the movable stage; and atleast one movable member installed in the vacuum chuck, the movablemember being operable to move up and down in the vacuum chuck to coupleand decouple the substrate with the vacuum chuck, wherein the sliding ofthe substrate on the movable stage is prevented by the adhering force ofthe vacuum chuck.